How to Calculate Gas Costs for Your Next Road Trip

Road trips can be expensive, but they don't have to be. Find out how much gas you'll use on your next road trip and get tips on saving money on gas prices.

With the pandemic shutting the doors to much of the world, Americans en masse have been packing up their cars and heading out to discover the beauty of National Parks and their own proverbial backyards. Some may know how to plan a road trip and use an American road trip guide to help, but others may be new to it and not know what to expect—especially when it comes to the cost of gas. All that driving can lead to surprise bills at the end of the month because of the varying prices of gas during your road trips. Here’s how to calculate gas costs ahead of time, save money on gas while on the road, and make your dollar stretch as far as possible while driving.

Calculate miles per gallon

As you plan for your road trip, you may be wondering, “How do you calculate gas cost per mile?”

The first thing you’ll want to do is figure out how many miles per gallon you are getting from your vehicle. To calculate miles per gallon, simply check your car’s owner’s manual to discover your gas tank size and then fill it up to the brim with gas (using a helpful gas finder app to ensure you’re getting the best price—see below!) These are the most fuel-efficient cars on the road.

Next, reset your trip odometer and start driving your usual mix of highway and city roads. When you get to “E” with a low mile range left, divide the total gallons your car holds by the miles you have driven. For example: 360 miles traveled on 15 gallons of gas = 24 miles per gallon (mpg) of fuel economy. The higher the mpg, the more fuel-efficient your car is and the less money you’ll spend on gas during your road trip.

Now, to calculate gas cost per mile simply divide the total miles driven by the total cost of your last fill-up. Using the prior example, if the gas cost $2.49 per gallon, your 15-gallon fill-up cost you $37.35. This equates to a rounded-down per mile cost of $.10 which can be calculated by doing this simple math:

360 miles / $37.35 = $.10


$2.49 / 24 mpg = $.10

infographic illustration outlinging the steps of how to calculate the amount that gas will cost on a road tripEmma Kumer/

Research trip distance

Whether you’re a fan of Google Maps or Waze, you should start your road trip planning with your smartphone in your hand to research trip distance and calculate gas costs then adjust your budget accordingly. You’ll likely enjoy your road trip more when driving one of the 18 best road trip cars.

Begin by entering your starting address and your final destination, then click “Add Stop” as often as needed to enter all the pit stops, sights to see, roadside attractions, and detours you plan to make along the way on your road trip. You’ll then be able to see the total miles of your entire road trip. If you have to drive more than you originally planned and are worried about your gas budget, you can make up for it in other ways. You can look for cheap places to stay and move some money around from your lodging budget to your gas budget.

“How much gas will I use?”

For example, if you now know that your total trip distance is an expected 2,325 miles and you’ve learned that your vehicle gives you 24 miles per gallon fuel economy, you simply divide the first number (2,325) by the second (24) to discover you’ll likely use 97 gallons of gas on your road trip.

2,325 miles / 24 mpg = 97 gallons of gas

Catherine Ryan Gregory of has a great tip to save money on gas while on a road trip. She points out that as you plan your stops and trip distance, that you think about consolidating your pit stops. This is because the more stops and starts your car makes, the less efficient it is and the higher cost of gas for the trip. For example, Gregory suggests that, “Instead of stopping for the bathroom, then a meal 45 minutes later, then gas 60 miles on the road, take care of all your tasks in one place whenever possible,” adding that, “You’ll save money and minimize your interaction with others, which reduces the risk of spreading COVID for you and the communities you pass through.” Need to rent a bigger or more fuel-efficient ride for your next vacation? Check out the best cars to rent for a road trip.

Price of gas

The GasBuddy app is the gold standard tool to find the best gas prices, says Gregory. The avid traveler and road trip pro notes that the app’s information is updated in real-time from other users, so you will know that the gas prices you see on the app are accurate. A gas trip estimator can help you save money on gas every day, whether commuting at home or on a long road trip, because gas prices fluctuate significantly, even when gas stations are right next to each other or straddle either side of state lines which is especially important to consider during a New England fall foliage road trip.

Yulia Safutdinova, founder of, relies on Google Maps for her solo road trips. She notes that not only does it allow her to avoid traffic and toll booths (helping keep her costs down), it also gives a bird’s eye view of all the gas stations along the route, as well as prices per gallon and opening hours. Safutdinova says using Maps to help lower the cost of gas for a trip is easy, “Just type in the word ‘gas’ and your fuel budget will be taken care of. The most important thing to remember, however, is to not just fill up your tank at the nearest station to you. Make sure to check all the prices and opt for the cheapest.” Make sure you read through these road trip planning tips before you leave!

Formula for “trip cost”

Because you’ve been able to easily calculate your car’s mpg, use map apps to find your road trip distance, and learned how to find the cheapest gas prices along your route, the next and final step is to discover how to calculate gas cost for the whole of your journey. Using the same example of a 2,325 road trip requiring 97 gallons of gas, take an eyeballed rough average of the gas prices the Gas Buddy or Gas Guru apps or Google Maps shows you’ll be paying along your route. Let’s say that the average gas price you’ll encounter during your road trip is $2.19:

97 gallons x $2.19 = $212.43 in gas cost for the duration of your trip

Of course, you should budget to spend a bit more gas than this because you’ll likely encounter unexpected stop-and-go traffic and time spent idling waiting for your little kids to pee at rest stops or while changing diapers on the side of the road (both of which will reduce your fuel-efficiency) and make fun detours that weren’t on your original itinerary putting more miles on your car. Need road trip inspiration? These are the best road trips in America.

Best gas trip estimators

Be sure to download these popular gas trip estimators before heading off on your next road trip.

Gas Buddy

With “GasBack” rewards and a promise to save you up to 25¢ per gallon on every fill-up, Gas Buddy is the leader in gas trip estimation for everyday use and especially during long road trips. Spend the money you save on these top road trip snacks.

Gas Guru

Another popular app for finding the cheapest gas in your current location or along your road trip route, Gas Guru helps to ensure that you never pay too much for gas again. This app will also help you calculate the cost of gas for a trip before you even start driving.

Google Maps

If you’re an Android user, Google Maps is likely already on your phone but if not, download it now. With Google Maps you’ll not only be able to find alternate routes should traffic be up ahead on your road trip (and even have them recommended to you to save you time, miles and therefore money on gas costs) but the prices of gas at stations along your journey and open/close times of each to guarantee that your tank is always full at the best possible price per gallon around.

This page on the Department of Energy’s website is the official U.S. government source for fuel economy information. With pre-loaded EPA estimated mpg data for thousands of vehicles, simply select your car’s year, make, and model then input start and end locations, plus any stops, and predicted percentage of city driving along the way to discover not only your combined mpg during your road trip but also the estimated calculated gas cost.

Toll Guru

When you want to calculate gas costs, fuel efficiency, and the price of the tolls you will encounter during your road trip including any discounts available when using toll tags like EZ-Pass and SunPass, Toll Guru is one of the best sites (with an accompanying app) to use.

Gas trip estimator apps are crucial to saving money on a road trip but don’t forget to download these other road trip planner apps, too.


Seaside road approaching a beach, seen from aboveMaxiphoto/Getty Images

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Jeff Bogle
Jeff Bogle is an Iris Award–winning photographer, avid traveler and English football fanatic who regularly covers travel, culture, cars, health, business, the environment and more for Reader's Digest. He is the proud dad of teen daughters.